digikam from trunk:
Use KProcess for RAW image loader.
Loading can now be cleanly aborted.

This is a good example that KProcess is not the perfect tool for use
with our shiny new multithreaded loader because KProcess is not reentrant,
but there are more advantages (wraps all system programming) so that
the necessary main thread indirections are ok.

TODO:
- implement fast loading specified in RAWDecodingSettings
- do we need to parse StdErr?